Wire Routing - Siemens m50 Series User Manual

d) To save money on cable, never use inferior cable that doesn't conform to EIA
standards and never eliminate the shield. To save money, many wholesale
wire makers will manufacture large rolls of cable on wooden spools to your
specifications at greatly reduced prices. When ordering wire simply specify:
"Equivalent to Belden Number XXXX", where "XXXX" is the wire type
recommended for the EIA specification.
e) Next, there is the question as to whether to connect Equipment Ground to DC
Ground of the power supply. Many pieces of electronic equipment have a
jumper that allows the DC Ground of the power supply outputs to be
connected to Equipment Ground, if desired. The EPAC M50-Series has no
such internal connections from Equipment Ground to DC Ground. Thus, by
following steps a) through d) above, the two are not connected. Siemens
recommends connecting the DC Ground of the cabinet power supply
(connector "A" pin W for EPAC M52) to the Equipment Ground in one place.
This connection will drain noise from the EPAC M50-Series circuitry. Keep in
mind that the cabinet power supply is electrically isolated from all of the
communications
communications port is floating. This is the Siemens recommended way to
install a system and you will have no problems with this practice. However,
in extremely noisy environments, the communications circuitry can pick up
so much noise it may be beneficial to connect the EIA Ground to Equipment
Ground to drain noise from the communications circuitry. This practice
results in a quieter system but can have devastating results if installed
incorrectly. Keep in mind that if the EIA Ground is tied to the Equipment
Ground in more than one place, the ground jumps will now send hundreds of
amps of current through the EPAC M50-Series circuit boards, from one
COMM connector to another. If severe communications noise is present,
carefully try connecting EIA Ground of one single COMM connector of one
single device on the COMM line to the Equipment Ground, and note whether
this reduces the number of errors in the communications log.
f) Lastly, be aware that most desktop or tower-style personal computers tie
their EIA Ground to Equipment Ground inside the computer. Many a
personal computer (and controller) has been destroyed by plugging the
COM1 port of the personal computer into a controller that has EIA Ground
connected to Equipment Ground. This creates a ground jump path through
the circuit boards of both the controller and personal computer. To avoid
problems, either the EIA Ground of all of the communications lines must be
floating, or the ground prong of the personal computer power cord must be
floating. Battery-powered notebook computers are not a problem, and are
the best choice for this application.

9.5.3 Wire Routing

Careful wire dress and wire routing, as described below will greatly reduce noise
problems:
AUGUST 2005
EPAC300-M50 SERIES USER'S MANUAL
lines, meaning that the EIA Ground of each
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